The present invention relates to a hydraulically entangled nonwoven composite fabric containing pulp fibers and a method for making a nonwoven composite fabric.
Although nonwoven webs of pulp fibers are known to be absorbent, nonwoven webs made entirely of pulp fibers may be undesirable for certain applications such as, for example, heavy duty wipers because they lack strength and abrasion resistance. In the past, pulp fiber webs have been externally reinforced by application of binders. For example, binders may be printed onto one or more sides of a wet laid web of pulp fibers to provide an absorbent wiper having strength and abrasion resistance. Typically, such externally reinforced wipers have contained up to about 25 percent, by weight, binder. Such high levels of binders can add expense and leave streaks during use which may render a surface unsuitable for certain applications such as, for example, automobile painting. Binders may also be leached out when such externally reinforced wipers are used with certain volatile or semi-volatile solvents.
Pulp fibers and/or pulp fiber webs have also been combined with materials such as, for example, nonwoven spunbonded webs, meltblown webs, scrim materials, and textile materials. One known technique for combining these materials is by hydraulic entangling. For example, U.S. Pat. No. 4,808,467 to Suskind discloses a high-strength nonwoven fabric made of a mixture of wood pulp and textile fibers entangled with a continuous filament base web.
Laminates of pulp fibers with textiles and/or nonwoven webs are disclosed in Canadian Patent No. 841,398 to Shambelan. According to that patent, high pressure jet streams of water may be used to entangle an untreated paper layer with base webs such as, for example, a continuous filament web.
European patent application 128,667 discloses an entangled composite fabric having an upper and lower surface. The upper surface is disclosed as having been formed of a printed re-pulpable paper sheet. The other surface is disclosed as having been formed from a base textile layer which may be, for example, a continuous filament nonwoven web. According to that patent application, the layers are joined by entangling the fibers of the pulp layer with those of the base layer utilizing columnar jets of water.
While these references are of interest to those practicing water-jet entanglement of fibrous materials, they do not address the need for a high pulp content nonwoven composite fabric which has strength and abrasion resistance and which may be used as a high strength wiper. There is still a need for an inexpensive high strength wiper which is able to quickly absorb several times its weight in water, aqueous liquid or oil. There is also a need for a high pulp content reinforced wiper which contains a substantial proportion of low-average fiber length pulp and which is able to quickly absorb several times its weight in water, aqueous liquid or oil. A need exists for a high pulp content composite fabric that can be used as a wiper or as a fluid distribution layer and/or absorbent component of an absorbent personal care product. There is also a need for a practical method of making a high pulp content nonwoven composite fabric. This need also extends to a method of making such a composite fabric which contains a substantial proportion of low-average fiber length pulp. Meeting this need is important since it is both economically and environmentally desirable to substitute low-average fiber length secondary (i.e., recycled) fiber pulp for high-quality virgin wood fiber pulp and still provide a high pulp content composite fabric that can be used as a wiper or as a fluid distribution layer and/or absorbent component of an absorbent personal care product.
The term xe2x80x9cmachine directionxe2x80x9d as used herein refers to the direction of travel of the forming surface onto which fibers are deposited during formation of a nonwoven web.
The term xe2x80x9ccross-machine directionxe2x80x9d as used herein refers to the direction which is perpendicular to the machine direction defined above.
The term xe2x80x9cpulpxe2x80x9d as used herein refers to fibers from natural sources such as woody and non-woody plants. Woody plants include, for example, deciduous and coniferous trees. Non-woody plants include, for example, cotton, flax, esparto grass, milkweed, straw, jute hemp, and bagasse.
The term xe2x80x9caverage fiber lengthxe2x80x9d as used herein refers to a weighted average length of pulp fibers determined utilizing a Kajaani fiber analyzer model No. FS-100 available from Kajaani Oy Electronics, Kajaani, Finland. According to the test procedure, a pulp sample is treated with a macerating liquid to ensure that no fiber bundles or shives are present. Each pulp sample is disintegrated into hot water and diluted to an approximately 0.001% solution. Individual test samples are drawn in approximately 50 to 100 ml portions from the dilute solution when tested using the standard Kajaani fiber analysis test procedure. The weighted average fiber length may be expressed by the following equation:       ∑                  x        i            =      0        k    ⁢            (                        x          i                *                  n          i                    )        /    n  
where k=maximum fiber length
xi=fiber length
ni=number of fibers having length xi 
n=total number of fibers measured.
The term xe2x80x9clow-average fiber length pulpxe2x80x9d as used herein refers to pulp that contains a significant amount of short fibers and non-fiber particles. Many secondary wood fiber pulps may be considered low average fiber length pulps; however, the quality of the secondary wood fiber pulp will depend on the quality of the recycled fibers and the type and amount of previous processing. Low-average fiber length pulps may have an average fiber length of less than about 1.2 mm as determined by an optical fiber analyzer such as, for example, a Kajaani fiber analyzer model No. FS-100 (Kajaani Oy Electronics, Kajaani, Finland). For example, low average fiber length pulps may have an average fiber length ranging from about 0.7 to 1.2 mm. Exemplary low average fiber length pulps include virgin hardwood pulp, and secondary fiber pulp from sources such as, for example, office waste, newsprint, and paperboard scrap.
The term xe2x80x9chigh-average fiber length pulpxe2x80x9d as used herein refers to pulp that contains a relatively small amount of short fibers and non-fiber particles. High-average fiber length pulp is typically formed from certain non-secondary (i.e., virgin) fibers. Secondary fiber pulp which has been screened may also have a high-average fiber length. High-average fiber length pulps typically have an average fiber length of greater than about 1.5 mm as determined by an optical fiber analyzer such as, for example, a Kajaani fiber analyzer model No. FS-100 (Kajaani Oy Electronics, Kajaani, Finland). For example, a high-average fiber length pulp may have an average fiber length from about 1.5 mm to about 6 mm. Exemplary high-average fiber length pulps which are wood fiber pulps include, for example, bleached and unbleached virgin softwood fiber pulps.
As used herein, the term xe2x80x9cspunbonded filamentsxe2x80x9d refers to small diameter continuous filaments which are formed by extruding a molten thermoplastic material as filaments from a plurality of fine, usually circular, capillaries of a spinnerette with the diameter of the extruded filaments then being rapidly reduced as by, for example, eductive drawing and/or other well-known spun-bonding mechanisms. The production of spun-bonded nonwoven webs is illustrated in patents such as, for example, in U.S. Pat. No. 4,340,563 to Appel et al., and U.S. Pat. No. 3,692,618 to Dorschner et al. The disclosures of these patents are hereby incorporated by reference.
As used herein, the term xe2x80x9cconjugate spun filamentsxe2x80x9d refers to spun filaments and/or fibers composed of multiple filamentary or fibril elements. Exemplary conjugate filaments may have a sheath/core configuration (i.e., a core portion substantially or completely enveloped by one or more sheaths) and/or side-by-side strands (i.e., filaments) configuration (i.e., multiple filaments/fibers attached along a common interface). Generally speaking, the different elements making up the conjugate filament (e.g., the core portion, the sheath portion, and/or the side-by-side filaments) are formed of different polymers and spun using processes such as, for example, melt-spinning processes, solvent spinning processes and the like. Desirably, the conjugate spun filaments are formed from thermoplastic polymers utilizing a melt-spinning process such as a spunbond process adapted to produce conjugate spunbond filaments.
As used herein, the term xe2x80x9csoftening pointxe2x80x9d refers to a temperature near the melt transition of a generally thermoplastic polymer. The softening point occurs at a temperature near or just below the melt transition and corresponds to a magnitude of phase change and/or change in polymer structure sufficient to permit relatively durable fusing or bonding of the polymer with other materials such as, for example, cellulosic fibers and/or particulates. Generally speaking, internal molecular arrangements in a polymer tend to be relatively fixed at temperatures below the softening point. Under such conditions, many polymers are difficult to soften so they creep, flow and/or otherwise distort to integrate or merge and ultimately fuse or bond with other materials. At about the softening point, the polymer""s ability to flow is enhanced so that it can be durably bonded with other materials. Generally speaking, the softening point of a generally thermoplastic polymer can be characterized as near or about the Vicat Softening Temperature as determined essentially in accordance with ASTM D 1525-91. That is, the softening point is generally less than about the polymer""s melt transition and generally about or greater than the polymer""s Vicat Softening Temperature.
As used herein, the term xe2x80x9clow-softening point componentxe2x80x9d refers to one or more thermoplastic polymers composing an element of a conjugate spun filament (i.e., a sheath, core and/or side-by-side element) that has a lower softening point than the one or more polymers composing at least one different element of the same conjugate spun filament (i.e., high-softening point component) so that the low-softening point component may be substantially softened, malleable or easily distorted when at or about its softening point while the one or more polymers composing the at least one different element of the same conjugate spun filament remains relatively difficult to distort or reshape at the same conditions. For example, the low-softening point component may have a softening point that is at least about 20xc2x0 C. lower than the high-softening point component.
As used herein, the term xe2x80x9chigh-softening point componentxe2x80x9d refers to one or more polymers composing an element of a conjugate spun filament (i.e., a sheath, core and/or side-by-side) that has a higher softening point than the one or more polymers composing at least one different element of the same conjugate spun filament (i.e., low-softening point component) so that the high-softening point component remains relatively undistortable or unshapeable when it is at a temperature under which the one or more polymers composing at least one different element of the same conjugate spun filament (i.e., the low-softening point component) are substantially softened or malleable (i.e., at about their softening point). For example, the high-softening point component may have a softening point that is at least about 20xc2x0 C. higher than the low-softening point component.
The present invention addresses the needs discussed above by providing a high pulp content nonwoven composite fabric. The composite fabric contains more than about 70 percent, by weight, pulp fibers which are hydraulically entangled into a nonwoven continuous filament substrate that makes up less than about 30 percent, by weight, of the fabric. For example, the nonwoven composite fabric may contain from about 5 to about 25 percent, by weight of the nonwoven continuous filament substrate and from about 75 to about 95 percent, by weight, pulp fibers. As another example, the nonwoven composite fabric may contain from about 10 to about 25 percent, by weight of the nonwoven continuous filament substrate and from about 75 to about 90 percent, by weight, pulp fibers.
The continuous filament nonwoven substrate may be a nonwoven layer or web of conjugate spun filaments. Desirably, the conjugate spun filaments are conjugate melt-spun filaments. The conjugate spun filaments are composed of at least one low-softening point component and at least one high-softening point component such that at least some exterior surfaces of the filaments composed of at least one low-softening point component. As an example, the conjugate spun filaments may include from about 20 to about 85 percent, by weight, of the high-softening point component and from about 15 to about 80 percent, by weight, of the low-softening point component. As another example, the conjugate spun filaments may include from about 40 to about 75 percent, by weight, of the high-softening point component and from about 25 to about 60 percent, by weight, of the low-softening point component. The high-softening point component may be, for example, polyesters, polyamides and/or high-softening point polyolefins (e.g., polypropylenes and propylene copolymers). The low-softening point thermoplastic component may be, for example, low-softening point polyolefins (e.g., polyethylenes and ethylene copolymers), low-softening point elastomeric block copolymers, and blends of the same.
The nonwoven layer or web of conjugate spun filaments may be a nonwoven layer or web of conjugate spunbond filaments. The conjugate spunbond filaments may have a sheath/core configuration. Alternatively and/or additionally, the conjugate spunbond filaments may have a side-by-side configuration. The nonwoven layer or web of conjugate spunbond filaments may include crimped filaments or the conjugate spunbond filaments may be crimped filaments.
According to an embodiment of the invention, the high pulp content nonwoven composite fabric may contain: 1) at least one nonwoven layer or web of conjugate spun filaments composed of at least one low-softening point component and at least one high-softening point component such that at least some exterior surfaces of the filaments are composed of at least one low-softening point component; 2) a fibrous component consisting of pulp fibers; and 3) regions in which the low-softening point component at the exterior surfaces of the filaments is fused to at least a portion of the fibrous component.
The nonwoven composite fabric may contain from about 0 up to about 30 percent, by weight, of the nonwoven layer or web of conjugate spun filaments and more than about 70 percent, by weight, of a fibrous component consisting of pulp fibers. For example, the nonwoven composite fabric may contain from about 5 to about 25 percent, by weight, of the nonwoven layer or web of conjugate spun filaments and from about 75 to about 95 percent, by weight, pulp fibers. As another example, the nonwoven composite fabric may contain from about 10 to about 25 percent, by weight of the nonwoven layer or web of conjugate spun filaments and from about 75 to about 90 percent, by weight, pulp fibers.
According to the present invention, the nonwoven layer or web of conjugate spun filaments may be entirely or substantially unbonded prior to being hydraulically entangled with the fibrous layer composed of pulp fibers.
In one aspect of the present invention, the nonwoven continuous filament substrate may have a total bond area of less than about 30 percent (as determined by optical microscopic methods) and a bond density greater than about 100 pin bonds per square inch. For example, the nonwoven continuous filament substrate may have a total bond area from about 2 to about 30 percent and a bond density of about 100 to about 500 pin bonds per square inch. As a further example, the nonwoven continuous filament substrate may have a total bond area from about 5 to about 20 percent and a bond density of about 250 to 350 pin bonds per square inch.
The pulp fiber component of the composite nonwoven fabric may be woody and/or non-woody plant fiber pulp. The pulp may be a mixture of different types and/or qualities of pulp fibers. For example, one embodiment of the invention includes a pulp containing more than about 50% by weight, low-average fiber length pulp and less than about 50% by weight, high-average fiber length pulp (e.g., virgin softwood pulp). The low-average fiber length pulp may be characterized as having an average fiber length of less than about 1.2 mm. For example, the low-average fiber length pulp may have a fiber length from about 0.7 mm to about 1.2 mm. The high-average fiber length pulp may be characterized as having an average fiber length of greater than about 1.5 mm. For example, the high-average fiber length pulp may have an average fiber length from about 1.5 mm to about 6 mm. One exemplary fiber mixture contains about 75 percent, by weight, low-average fiber length pulp and about 25 percent, by weight, high-average fiber length pulp.
According to the invention, the low-average fiber length pulp may be certain grades of virgin hardwood pulp and low-quality secondary (i.e., recycled) fiber pulp from sources such as, for example, newsprint, reclaimed paperboard, and office waste. The high-average fiber length pulp may be bleached and unbleached virgin softwood pulps.
The present invention also contemplates treating the nonwoven composite fabric with small amounts of materials such as, for example, binders, surfactants, cross-linking agents, de-bonding agents, fire retardants, hydrating agents and/or pigments. Alternatively and/or additionally, the present invention contemplates adding particulates such as, for example, activated charcoal, clays, starches, and superabsorbents to the nonwoven composite fabric.
The nonwoven composite fabric may be used as a heavy duty wiper or as a fluid distribution material in an absorbent personal care product. In one embodiment, the nonwoven composite material may be a single-ply or multiple-ply wiper having a basis weight from about 20 to about 200 grams per square meter (gsm). For example, the wiper may have a basis weight between about 25 to about 150 gsm or more particularly, from about 30 to about 110 gsm. The wiper desirably has a water capacity greater than about 450 percent, an oil capacity greater than about 250 percent, a water wicking rate (machine direction) greater than about 2.0 cm per 15 seconds, and oil wicking rate (machine direction) greater than about 0.5 cm per 15 seconds. When used as a fluid management material in a personal care product, the nonwoven composite fabric may have about the same properties as the wiper embodiment except for a basis weight which may range from about 40 to about 170 gsm, for example, from about 60 to about 120 gsm. Additionally, one or more layers of the nonwoven composite fabric may be used as an absorbent component of a personal care product, especially with added superabsorbent material. When used as an absorbent component, the nonwoven composite fabric may have a basis weight of 100 gsm or more and may also serve as a fluid distribution material. For example, the nonwoven composite material may have a basis weight from about 100 to about 350 gsm.
The present invention also contemplates a method of making a high pulp content nonwoven composite fabric by superposing a pulp fiber layer over a nonwoven continuous filament substrate having a total bond area of less than about 30 percent and a bond density of greater than about 100 pin bonds per square inch; hydraulically entangling the layers to form a composite material; and then drying the composite.
According to the invention, the layers may be superposed by depositing pulp fibers onto the nonwoven continuous filament substrate by dry forming or wet-forming processes. The layers may also be superposed by overlaying the nonwoven continuous filament substrate layer with a coherent pulp fiber sheet. The coherent pulp fiber sheet may be, for example, a re-pulpable paper sheet, a re-pulpable tissue sheet or a batt of wood pulp fibers.
The hydraulically entangled nonwoven composite fabric may be dried utilizing a non-compressive drying process. Desirably, the drying step is carried out in a manner that simultaneously creates regions in which the low-softening point component at the exterior surfaces of the filaments is fused to at least a portion of the fibrous component. Through-air drying processes have been found to work particularly well. Other drying processes which incorporate infra-red radiation, yankee dryers, steam cans, vacuum de-watering, microwaves, and ultrasonic energy may also be used.